What are asteroids? How real is the threat of them causing extinction of life? What strategies have been developed to prevent such a catastrophe?

Asteroids are rocky and metallic remnants left over from the formation of the Solar System, mostly orbiting the Sun in the main belt between Mars and Jupiter. Those whose orbits bring them within striking distance of Earth are classified as Near-Earth Objects (NEOs), the focus of planetary-defence efforts.

How real is the threat?

• Large impacts are extremely rare but civilisation-altering: the Chicxulub impact about 66 million years ago is linked to the mass extinction that ended the dinosaurs.
• Smaller events do occur, as the 2013 Chelyabinsk airburst over Russia showed, shattering windows and injuring over a thousand people.
• Most catastrophic-sized (over 1 km) NEOs have already been catalogued and none pose a near-term collision risk, so the extinction threat is genuinely low-probability but high-consequence.

Strategies developed

• Detection and tracking: NASA's NEO surveys and its Planetary Defense Coordination Office, the UN-endorsed International Asteroid Warning Network, and upcoming space telescopes continuously catalogue and monitor NEOs to give early warning.
• Deflection: the kinetic-impactor approach was successfully demonstrated by NASA's DART mission (2022), which measurably altered the orbit of the asteroid moon Dimorphos; ESA's Hera mission will study the aftermath in detail.
• Other proposed techniques include the gravity tractor, ion-beam shepherding to nudge an asteroid over time, and, only as a last resort, nuclear stand-off deflection.
• Preparedness: international coordination through the Space Mission Planning Advisory Group and civil-defence planning for regional airburst events complement the technological effort.

Early detection gives the years of lead time that even a small nudge needs to translate into a safe miss. Combining early warning through sky surveys with a proven deflection capability like DART is making planetary defence increasingly credible, gradually turning a once-existential risk into a manageable one.